Platelet-derived growth factor receptors form complexes with neuropilin-1 during megakaryocytic differentiation of thrombopoietin-dependent UT-7/TPO cells.

Neuropilin-1 (NRP-1) is involved in angiogenesis, but the role of NRP-1 in megakaryocytopoiesis is not yet fully understood. In this study, we investigated whether thrombopoietin (TPO) regulates the expression of platelet-derived growth factor (PDGF) and its receptors (PDGFRs) on TPO-dependent UT-7/TPO cells and whether PDGFRs and NRP-1 on UT-7/TPO cells form complexes during megakaryocytic differentiation. When UT-7/TPO cells were starved of TPO for 24 h and then stimulated with 5 ng/ml TPO, the expression of PDGF-B, PDGFRα, and PDGFRβ were significantly up-regulated after the addition of TPO. TPO also induced tyrosine phosphorylation of PDGFRα but not PDGFRβ, and promoted the formation of PDGFRαβ heterodimer complexes. Furthermore, megakaryocytic differentiation of UT-7/TPO cells on treatment with phorbol myristate acetate (PMA) was accompanied by a marked up-regulation of PDGFRβ and NRP-1 protein expression, complex formation between PDGFRs and NRP-1, PDGFRαβ heterodimer complexes, and an increase in PDGF-BB-binding activity. Immunocytochemistry confirmed complex formation between PDGFRs and NRP-1 and PDGFRαβ heterodimer complexes in PMA-differentiated UT-7/TPO cells. Our observations suggest that NRP-1 is involved in megakaryocytopoiesis through complex formation with PDGFRs, and that NRP-1-PDGFR-complexes may contribute to effective cellular functions mediated by TPO and PDGF in megakaryocytic cells.